On the Origin and Office of the Alburnum of Trees. 303 



the alburnous tubes with a composition formed of calcined 

 oyster snells and cheese *, and this was covered with a mix- 

 ture or bees wax and turpentine, so as to effectually exclude 

 all moisture. A part of the bark was taken off each branch, 

 in a circle round it, a few lines distant from its lower end, 

 where the tubes had been closed ; and each branch was then 

 placed in a decoction of logwood, in a vessel d^ftp enough 

 to cover the decorticated spaces. At the end of twenty 

 hours, or somewhat longer periods, these branches Were 

 examined, and the coloured infusion was found to have in- 

 sinuated itself between the alournous tubes, in many in- 

 stances apparently through the cellular suhs'ance. This was 

 most obvious in the walnut tree, the youna; wood of which 

 is very white. The principal object I had in view in making 

 this experiment, was to detect the passages through which 

 I conceived the sap to pass from the bark into the alburnum f „ 



From the preceding c^cumstances, I am disposed to infer 

 that the sap secretes through the ..cellular substance of the 

 alburnum; and through this I conceive that it must ascend 

 when the tubes were intersected in the preceding experi- 

 ments, and in those seasons of the year when the alburnous 

 tubes are empty, though the sap must be rising with great 

 rapidity : and I shall endeavour to show that the presence 

 of the sap in the alburnous tubes, during that part of the 

 year in which trees, when wounded, bleed abundantly, does 

 not afford any decisive evidence of the ascent of the sap 

 through those tubes. 



In the last spring, when the buds of the sycamore first 

 betran to prepare for unfolding, I found that the sap abound- 

 ed in the points at the annual branches ; and at the same 

 time it flowed abundantly from incisions made into the al- 

 burnum near the root. But when similar incisions were 

 made at the distance of eight or ten feet from the ground- 1 ', 

 not the least muisture flowed; and the tubes of the albur- 



* I have found this composition, and this only, to he capable of instan- 

 taneously stopping the effusion of sap from the vine, or other tree, in the 

 bleeding season. 



| Philosophical Transaction's for 1807, p. 7. 



nam 



